Plant MutS2 proteins function in plastid ribosome quality control

Tight regulation of chloroplast translation is essential for plant growth, development and environmental response. Active translation can result in stalling and collision of ribosomes, which have negative fitness consequences. However, the ways in which chloroplasts respond to these types of translational stressors remain unknown. Here, we identify two MutS2 proteins that act as critical players in plastid ribosome-associated quality control (RQC) in Arabidopsis. We found that both MutS2A and MutS2B are required to overcome specific antibiotic-induced ribosome stalling and collisions. Further, these proteins appear to be essential for tissue greening during de-etiolation, potentially due to increased translational demand during the transition from etioplast to chloroplast. Although bacterial homologs of MutS2 have been widely recognized for their role in regulating homologous recombination, we found only weak support for this function in Arabidopsis plastids. Therefore, these proteins, which are widely conserved among photosynthetic eukaryotes, appear to be central in the resolution of ribosome collisions and may play a critical role during times of increased translational demand.